For combat I always use a grid. Always.
Theatre of the mind combat is extremely frustrating and limiting because no matter how smart you are, or think you are, you cannot account for everything, and many abilities in D&D (old and new school) require very specific knowledge of positioning.
That doesn't mean you can't use what's on the grid to offer some ToTM flavour, for instance. When I run my 1e games, where combat rounds are meant to take place over the course of a minute, I often offer a descriptive based on how the dice roll, or decisions made by enemies - things like that. It's still informative, but the grid is always the baseline.
For roleplaying scenarios, ToTM will win out, I don't feel the need to draw every nuance of the tavern the players are in (unless I'm expecting trouble, or the players start instigating something) for everything. I still often stand when I DM and gesture, act, do voices etc to aid in that.
So in short, I definitely feel a mix of theatre of the mind and grid play are essential. But combat without a grid to track positions, ranges, cover, etc etc... that's a non-starter.